Recent electronic apparatuses include an electric/electronic part, and a plurality of axial flow fans for cooling the electric/electronic part. For example, two axial flow fans are arranged side-by-side in a common duct. In this case, if one axial flow fan stops due to a problem, the entire cooling ability greatly drops because the axial flow fan cannot discharge the cooling air but also the cooling air discharged by another axial flow fan can reversely flow through the stopped axial flow fan. Therefore, there is a proposal to arrange a reverse flow preventing device on the discharge side of an axial flow fan, so that if one axial flow fan stops, the cooling air-discharged by another axial flow fan does not reversely flow through the stopped axial flow fan.
For example, Japanese Unexamined Patent Publication (Kokai) No. 50-95802 discloses a fan unit comprising an axial flow fan and a reverse flow preventing plate of a plastic sheet arranged on the discharge side of the axial flow fan. A portion of the reverse flow preventing plate is fixed to the fan unit and the remaining portion of the reverse flow preventing plate is elastically deformable. When the axial flow fan is operated, the reverse flow preventing plate elastically deforms, upon receiving the force produced by the axial flow fan, whereby a flow passage is formed between the axial flow fan and the reverse flow preventing plate. When the axial flow fan is stopped, the axial flow fan does not generate a flow of air and the reverse flow preventing plate returns to a position in which it covers the axial flow fan. Therefore, a flow of air which is apt to reversely flow through the axial flow fan is blocked by the reverse flow preventing plate.
In the case of the reverse flow preventing plate disclosed by this prior art, there is a problem in that the reverse flow preventing plate flaps in the flow of air produced by the axial flow fan while the axial flow fan is operated, and noise is produced.
Japanese Unexamined Patent Publication (Kokai) No. 9-126191 discloses an axial flow fan structure in which blades of the axial flow fan are constructed so as to have a functions of a fan itself and a function of a reverse flow prevention. The blades of the axial flow fan are movably attached to the rotation shaft of the axial flow fan via hinges. When the axial flow fan is operated, the blades of the axial flow fan move to a position in which they take a usual, generally spiral blade shape. When the axial flow fan is stopped, the blades of the axial flow fan move to a position in which they are generally perpendicular to the rotation axis, to thereby close the flow passage of the axial flow fan. It is difficult to fabricate the blades of the axial flow fan disclosed by this prior art, and there are problems of noise and cost if the blades are fabricated.
Japanese Unexamined Patent Publication (Kokai) No. 11-22698 discloses a fan device comprising an axial flow fan, and a reverse flow preventing device including louver-shaped plate members. In this case, all the louver-shaped plate members are arranged parallel to each other and form flow passages opening in constantly inclined directions relative to the axial flow fan, so the flow of air produced by the axial flow fan becomes a flow which is deflected in one direction, and problems of the reduction of the fan performance and the increase in noise occur.